Bone up on calcium.

During childhood and adolescence, the body uses calcium to build strong bones—a process that's all but complete by the end of the teen years. Getting enough calcium at a young age is important to prevent osteoporosis later on. Yet more than 85 percent of girls and 60 percent of boys aged 9 to 18 fail to get the recommended 1,300 milligrams of calcium per day (kids aged 4 to 8 years old need 800 mg; toddlers aged 1 to 2 years need 500 mg). The 2005 Dietary Guidelines recommend 2 cups of low-fat or nonfat milk or dairy products per day for children 2 to 8 years old and 3 cups for children 9 years and older.